.register{
    position: absolute;
    top:0;
    right: 0;
    left: 0;
    bottom: 0;
    margin: auto;
    width: 200px;
    height: 200px;
}
.black{
    width: 100vw;
    height: 100vh;
    position: fixed;
    top:0;
    left: 0;
    z-index: 100;
    background: rgba(0,0,0,0.6);    
}
.black .fff{
    width: 200px;
    height: 200px;
    margin: 200px auto;
    background-color: #fff;
}